This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 arising from an application for a Optical Fiber For Optical Amplifier earlier filed in the Korean Industrial Property Office on Jan. 20, 1999 and there duly assigned Serial No. 1647/1999.
1. Field of the Invention
The present invention relates to optical fibers for use in optical amplifiers, and more particularly, to an optical fiber for use in an optical amplifier, which contains dysprosium ion (Dy3+) and has an improved light amplification efficiency at a 1.31 xcexcm band.
2. Description of the Related Art
In the manufacture of optical amplifiers used to amplify an optical signal having a wavelength of 1.31 xcexcm which belongs to the zero dispersion wavelength of silica glass, rare earth elements, for example, neodymium (Nd), praseodymium (Pr) or dysprosium (Dy) in the form of ions, are commonly implanted into a glass base. However, in the case of doping the glass with Nd3+, fluorescence is emitted at a wavelength of 1.31 xcexcm, which is considerably far from the zero dispersion wavelength, during the transition of 4F3/2xe2x86x924/13/2 of Nd3+. The intensity of fluorescence emitted at the 4F3/2 level is very weak at a wavelength of 1.31 xcexcm, compared to at other wavelengths, for example, at 890 nm and 1064 nm. Also, due to excited state absorption at the 4F3/2 level, optical gain decreases at a wavelength shorter than 1.36 xcexcm. To account for these problems, a fluoride-rich glass has been suggested as a base material, instead of the silica glass. However, the use of the fluoride-rich glass fails to increase the optical gain to a desired level at the wavelength of 1.31 xcexcm.
Also, Pr3+, as a rare earth element implanted into a glass in optical fiber manufacture, permits the utilization of fluorescence emission by the transition of 1G4xe2x86x923H5. Such a transition is more likely to occur than at other energy levels, and thus a high optical amplification efficiency is expected when Pr3+ is used as a doping material.
However, the energy difference between the 1G4 and 3F5 levels is very small at3000 cmxe2x88x921, and thus in using an oxide glass having a high lattice vibration energy of 800 cmxe2x88x921 as a base material, there is a high possibility of nonradiative transition occurring by Pr3+ excited to the 1G4 level due to it multiple lattice vibration relaxation. As a result, the light amplification efficiency decreases rather than increases. Thus, in using Pr3+ for the purpose of increasing the optical amplification efficiency in the manufacture of optical amplifiers, a base material having a low lattice vibration energy should be accompanied with Pr3+.
A fluoride glass containing ZrF4 is widely known as a base material having a low lattice vibration energy. However, such fluoride glass has a low quantum efficiency at 4% or less, and thus it is difficult to obtain satisfactory performance in view of fluorescence lifetime. For this reason, research into use of a sulfide glass which has a lower lattice vibration energy than a fluoride glass, as a base material, has actively conducted.
U.S. Pat. No. 5,321,708 for an Optical Fiber Amplifier Doped With Dysprosium Ion For The 1.3 xcexcm Wavelength Band to Tohmon et al and U.S. Pat. No. 5,694,500 for an Optical Amplifier Operating at 1.3 Microns Useful For Telecommunications And Based On Dysprosium-Doped Metal Chloride Host Materials to Page et al disclose the use of trivalent Dysprosium ions as a dopant for amplification of 1.31 xcexcm wavelengths in optical amplifiers. However, I have not seen the use of dysprosium ions as a dopant for germanium-gallium-sulfide glass or for germanium-gallium-arsenic-sulfide glass.
An object of the present invention is to provide an optical fiber for use in optical amplifiers, which contains dysprosium ions (Dy3+) and has an improved light amplification efficiency at a wavelength of 1.31 xcexcm.
The object of the present invention is achieved by an optical fiber for an optical amplifier, comprising a germanium-gallium-sulfide (Gexe2x80x94Gaxe2x80x94S) glass, an alkali metal halide, and dysprosium (Dy) as a rare earth element.
Preferably, the content of alkali metal halide is in the range of approximately 1 to 20 mol % based on the total amount of Gexe2x80x94Gaxe2x80x94S glass and alkali metal halide, and the content of rare earth element is in the range of 0.01 to 0.1 at % based on the total amount of Gexe2x80x94Gaxe2x80x94S glass, alkali metal halide and rare earth element. Preferably, the alkali metal halide is KBr, CsBr, KI or CsI.
When KBr or CsBr is used as the alkali metal halide, an improvement of fluorescence lifetime at the 1.31 xcexcm band is excellent regardless of the content of alkali metal halide. It is more preferable that the alkali metal halide content is greater than or equal to the Ga content, in view of the improvement of fluorescence lifetime.
When the alkali metal halide is KI or CsI, it is preferable that the Ga content in the Gexe2x80x94Gaxe2x80x94S glass is 10 at % or more based on the total composition of the glass, for more improvement of the fluorescence lifetime at the 1.31 xcexcm band. It is more preferable that the alkali metal halide content is greater than or equal to the Ga content, in view of the fluorescence lifetime increase at the 1.31 xcexcm band.
It The object of the present invention is achieved by an optical fiber for an optical amplifier, comprising a germanium-gallium-arsenic-sulfide (Gexe2x80x94Gaxe2x80x94Asxe2x80x94S) glass, an alkali metal halide, and dysprosium (Dy) as a rare earth element.
Preferably, the content of alkali metal halide is in the range of approximately 1 to 20 mol % based on the total amount of Gexe2x80x94Gaxe2x80x94Asxe2x80x94S glass and alkali metal halide, and the content of rare earth element is in the range of approximately 0.01 to 0.1 mol % based on the total amount of Gexe2x80x94Gaxe2x80x94Asxe2x80x94S glass, alkali metal halide and rare earth element.